1. Field of the Invention
The present invention relates to a resin composition for ink supply tubes and also relates to an ink supply tube.
2. Description of the Related Art
Conventional ink jet recording apparatuses make records on recording media in such a manner that inks are ejected from ink jet recording heads. In such an ink jet recording apparatus, a carriage equipped with an ink jet recording head is moved over a recording medium in a main scanning direction and ink is ejected from the ink jet recording head while moving to perform recording. After a main scan is performed once, the recording medium is moved by a certain amount in an auxiliary scanning direction and the carriage is moved in the main scanning direction again to perform recording. A desired pattern can be recorded on the recording medium by repeating this operation.
A type of ink supply unit for use in the ink jet recording apparatus is equipped with a replaceable tank (ink tank), filled with ink, separate from the carriage. In the ink jet recording apparatus, the ink tank is connected to the ink jet recording head, which is aboard the carriage, through an ink supply tube placed therebetween such that ink is supplied to the ink jet recording head. This type is suitable for the purpose of using a relatively large amount of ink because the volume of the ink tank can be readily increased.
When the ink jet recording apparatus is used for recording, the ink supply tube, which connects the ink tank to the ink jet recording head, is pulled or twisted due to the reciprocating motion of the carriage, which equipped with the ink jet recording head, and therefore is increased in flexural rigidity. If the ink supply tube has high hardness, fatigue failure may possibly occur therein. Therefore, the ink supply tube needs to have flexibility enough to cope with reciprocation. In particular, the ink supply tube needs to cope with reciprocation with a smaller curvature and needs to have higher flexibility because of the recent downsizing of ink jet printers.
If moisture evaporates from ink present in the ink supply tube to leak out of the ink supply tube, the viscosity of the ink therein will increase. This may cause serious problems such as improper ink ejection and a reduction in print quality due to the change in composition of the ink. In addition, if gases such as air permeate through the ink supply tube, the gases will dissolve in the ink in the ink supply tube to cause a reduction in the degree of deaeration of the ink or the creation and growth of bubbles in the ink. This may possibly cause improper ink ejection and a reduction in print quality. Therefore, the ink supply tube needs to have high moisture barrier performance and air barrier performance.
Japanese Patent Laid-Open No. 9-300652 discloses an ink supply tube for ink jet recording. This ink supply tube has a layered structure consisting of an inner layer in contact with ink, an outer layer in contact with air, and an intermediate layer made of a material with low gas permeability, the inner and outer layers being made of a material having ink resistance, low permeability, and low rigidity. In particular, the inner and outer layers are made of polyethylene and the intermediate layer is made of an ethylene-vinyl alcohol copolymer or polyvinylidene chloride.
Techniques for using highly flexible thermoplastic elastomers to prepare ink supply tubes for ink jet recording are being investigated. Such thermoplastic elastomers include olefinic thermoplastic elastomers, urethane thermoplastic elastomers, ester thermoplastic elastomers, styrenic thermoplastic elastomers, and polyvinyl chloride thermoplastic elastomers. In particular, the styrenic thermoplastic elastomers have excellent flexibility and rubber elasticity. Examples of the styrenic thermoplastic elastomers include styrene-butadiene-styrene (SBS) block copolymers, styrene-isoprene-styrene (SIS) block copolymers, styrene-ethylene-butylene-styrene (SEBS) block copolymers, and styrene-ethylene-propylene-styrene (SEPS) block copolymers. In recent years, styrene-isobutylene-styrene (SIBS) block copolymers have been developed.
Japanese Patent Laid-Open No. 2005-305878 discloses a resin composition, containing a thermoplastic elastomer, for ink jet recording. In particular, the resin composition contains a styrene-isobutylene-styrene (SIBS) block copolymer, a polyolefin, and liquid polybutene and has excellent gas barrier performance, excellent moisture barrier performance, and good flexibility.